scottiemedic :
You have to set up backup in the Accessories, System Tools folder
Thanks for that, but I realise that, trying to be succinct, I did not give the full details. It is not the external drive that appears to be not working but the software they provided, which is NTI Backup Now EZ, which something appears to be blocking (it always starts but I get a strandard MS error message after about 5 seconds and it stops). I assume that what you are suggesting is using a built-in Windows back-up programme, but will this do the same job, which is backing up daily by comparing present files with the last back-up and changing only those that are different? There is, no doubt, other software available that will do this, but I would prefer it if the one provided would work!